Monday, May 27, 2013

Spring Gun progress so far

I'm making progress, probably about 2/3 done with the basic prototype. The goal of this project is to make a prototype that I can experiment with, not something I expect to carry around. That means weight is a second priority to reconfigurability.

Because the device I'm making is small and complex, precision of parts is more important than any other metal-working project I've done before. I considered actually 3d printing many parts but concluded that in many cases they would not be strong enough to handle the forces involved.

In practice, my digital calliper and the milling-machine's measures were invaluable. I calculated the size and position of each part/cut/hole at the level of 1/16" and in practice I was able to measure that each was placed within 1/32" with the exception of welding. It's amazing how significantly a piece of metal will warp during welding. I have not yet figured out how to solve this.

As noted, this involved a lot of milling. Among other things, I found that ~300-400 RPM on the mill was a good speed for steel. At lower speeds I think my mill takes too much torque and sometimes vibrates significantly. At higher speeds it needs more cutting oil and seems to produce more metal slivers instead of metal ribbons.

The act of welding it required in many cases placing parts on top of other stand off pieces. In this sense I found it very helpful to have a variety of shims: 1/8" flats, 1/4", 1/2", 1" square bars.

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